The present invention is with respect to a printed board for electrical circuits and to a process for making it. The present invention is more specially in connection with a printed board made up of a board material covered with a copper layer in the form of printed wiring and a process for making printed boards in the case of which after coating the copper coated boards with etch resist in the form of desired wiring the etch resist is cured and the copper layer not covered by the etch resist is etched away.
Such printed boards for electrical circuits and such processes for making such boards have come into general use. The starting material is normally copper coated board, made for example of paper-resin laminate. By screen printing or spraying, for example, a pattern of etch resist is produced on the copper layer to take the form of the desired printed wiring. Furthermore photographic processes may be used, in which the copper layer is completely covered by the etch resist. In this case the etch resist is photosensitive and, after exposure through a mask representative of the printed wiring, undergoes development, the etch resist being then washed away at those positions at which the copper is then later to be etched.
Furthermore it is old for an uncoated, that is to say not copper coated board, to have electrically conducting lacquer, that is to say "resistance lacquer conducting lacquer" put on it by screen printing or some other process. Such lacquers as presently marketed however have the shortcoming that copper coated therewith may not be soldered so that for producing the printed circuit boards, which are then later to have the electrical components fixed to them, such a process may not be used, although however the components may be riveted in place, but this is a high-price operation. A further shortcoming of conducting lacquer is to be seen in its relatively high resistivity in comparison with copper printed wiring.
In the case of the copper coated boards with printed wiring noted earlier there is on the other hand the shortcoming that after etching, the etch resist has to be taken off again for uncovering the printed wiring for soldering. Furthermore the copper layer, once freed of the etch resist, is oxidized relatively quickly so that such oxide has to be cleaned off from the copper before any soldering.
For many uses it is best for certain switching functions to be undertaken on the printed board itself, for example by having an electrically conducting current which is able to be moved into and out of contact with a certain point on the printed wiring or, in other cases, ane part of the printed wiring may be joined up with other printed wiring near to it by moving electric contact. Because copper is quickly oxidized, the printed wiring has to be coated, at least at the contact points, with non-oxidizing electrically conducting material as for example gold, silver or nickel by electroplating, this making it necessary for the structure to be plated to be in one piece electrically, this not being true of most printed circuit structures. If, for keeping prices low, the contact coating material, as for example gold, is to be limited to the contact points only, in a separate working step certain parts of the printed wiring have to covered over or masked with a material which is resistant to the electroplating bath, this making further working steps necessary together with specially produced masks.